"Stockpile" of slight transcriptomic changes determines the indirect genotoxicity of low-dose BPA in thyroid cells

Epidemiological and experimental data highlighted the thyroid-disrupting activity of bisphenol A (BPA). Although pivotal to identify the mechanisms of toxicity, direct low-dose BPA effects on thyrocytes have not been assessed. Here, we report the results of microarray experiments revealing that the transcriptome reacts dynamically to low-dose BPA exposure, adapting the changes in gene expression to the exposure duration. The response involves many genes, enriching specific pathways and biological functions mainly cell death/proliferation or DNA repair. Their expression is only slightly altered but, since they enrich specific pathways, this results in major effects as shown here for transcripts involved in the DNA repair pathway. Indeed, even though no phenotypic changes are induced by the treatment, we show that the exposure to BPA impairs the cell response to further stressors. We experimentally verify that prolonged exposure to low doses of BPA results in a delayed response to UV-C-induced DNA damage, due to impairment of p21-Tp53 axis, with the BPA-treated cells more prone to cell death and DNA damage accumulation. The present findings shed light on a possible mechanism by which BPA, not able to directly cause genetic damage at environmental dose, may exert an indirect genotoxic activity

Loss of IL-10 signaling in macrophages limits bacterial killing driven by prostaglandin E2

Loss of IL-10 signaling in macrophages (Mφs) leads to inflammatory bowel disease (IBD). Induced pluripotent stem cells (iPSCs) were generated from an infantile-onset IBD patient lacking a functional IL10RB gene. Mφs differentiated from IL10RB−/− iPSCs lacked IL-10RB mRNA expression, were unable to phosphorylate STAT3, and failed to reduce LPS induced inflammatory cytokines in the presence of exogenous IL-10. IL-10RB−/− Mφs exhibited a striking defect in their ability to kill Salmonella enterica serovar Typhimurium, which was rescuable after experimentally introducing functional copies of the IL10RB gene. Genes involved in synthesis and receptor pathways for eicosanoid prostaglandin E2 (PGE2) were more highly induced in IL-10RB−/− Mφs, and these Mφs produced higher amounts of PGE2 after LPS stimulation compared with controls. Furthermore, pharmacological inhibition of PGE2 synthesis and PGE2 receptor blockade enhanced bacterial killing in Mφs. These results identify a regulatory interaction between IL-10 and PGE2, dysregulation of which may drive aberrant Mφ activation and impaired host defense contributing to IBD pathogenesis

The zebrafish model to identify new genes involved in thyroid development

Thyroid organogenesis is a very complex developmental process that leads to the formation of an organ able to produce specific hormones through specification, migration, structural organization and functional differentiation of thyroid precursor cells. In mammals, alteration of these mechanisms might be responsible for congenital hypothyroidism (CH), the most frequent inherited endocrine disease. Thyroid development in fish is comparable to mammals at both ontogenetic and molecular levels: the thyroid develops from the endodermal tissue, at the midline of the pharyngeal floor, and its formation is subdivided into main successive steps shared with mammals. The genetic program involved in fish thyroid differentiation, including the activity of transcription factors such as Nkx2.1a, Pax8 and Hhex, is conserved with respect to expression patterns and functions. To gain further insights on the genetic machinery implicated in normal thyroid development, and therefore in CH disease, an oligonucleotide microarray analysis was performed in mouse with the aim to identify genes differentially expressed during gland organogenesis. This approach highlighted a list of genes enriched in embryonic mouse thyroid. In the present work, the zebrafish model was used to perform functional analysis on fish counterparts of the murine thyroid enriched genes. Looking at the expression territories of the zebrafish orthologs, a very low correlation in thyroid expression profile between mouse and zebrafish was found: indeed, very few mouse thyroid expressed genes have their zebrafish ortholog being expressed in thyroid primordium. This observation strongly suggests that some changes concerning thyroid development occurred from lower to higher vertebrates; during evolution, the thyroid of higher vertebrates probably recruited new genetic pathways/functions by means of mutations occurred in cis-regulatory elements. Despite the low correlation in expression profiles, a new conserved function relevant for thyroid development was identified with this comparative approach; an anti-apoptotic function, represented by Bcl2 in mouse and bcl2l in zebrafish, was conserved during thyroid evolution. Knock-down experiments conducted by means of morpholinos injection, have revealed that bcl2l is regulated by the thyroid transcription factors and plays a relevant role in normal thyroid development. Indeed, bcl2l thyroid expression was lost in embryos deprived of the thyroid transcription factors, leading to thyroid degeneration via apoptosis. It is feasible to hypothesize that a conserved antiapoptotic function during thyroid evolution could counteract a putative proapoptotic function, ready to intervene if something fails during normal gland morphogenesis

Specific Effects of Chronic Dietary Exposure to Chlorpyrifos on Brain Gene Expression— A Mouse Study

Chlorpyrifos (CPF) is an organophosphate insecticide used to control pests on a variety of food and feed crops. In mammals, maternal exposure to CPF has been reported to induce cerebral cortex thinning, alteration of long-term brain cognitive function, and Parkinson-like symptoms, but the mechanisms of these processes are not fully understood. In this study, we aimed to gain a deeper understanding of the alterations induced in the brains of mice chronically exposed to CPF by dietary intake. For our purpose, we analysed F1 offspring (sacrificed at 3 and 8 months) of Mus musculus, treated in utero and postnatally with 3 different doses of CPF (0.1-1-10 mg/kg/day). Using RT2 Profiler PCR Arrays, we evaluated the alterations in the expression of 84 genes associated with neurodegenerative diseases. In the brains of exposed mice, we evidenced a clear dose–response relationship for AChE inhibition and alterations of gene expression. Some of the genes that were steadily down-regulated, such as Pink1, Park 2, Sv2b, Gabbr2, Sept5 and Atxn2, were directly related to Parkinson’s onset. Our experimental results shed light on the possibility that long-term CPF exposure may exert membrane signalling alterations which make brain cells more susceptible to develop neurodegenerative diseases

Bisphenol A interferes with thyroid specific gene expression

Bisphenol A (BPA) is an endocrine-disrupting chemical that leads to low-dose human exposure due to its ability to leach from chemically derived products, as polycarbonate plastics and epoxy resin. In addition to its known xeno-endocrine action, BPA exerts a wide range of metabolic effects. Despite the documented BPA exposure outcomes on synthesis of thyroid hormones, there are not any data available on its actions on the thyroid follicular cells, site of synthesis of the thyroid hormones. Recently, it has been shown that several environmental pollutants, as BPA, can exert a thyroid disrupting activity. In this study, we employed in vitro and in vivo (zebrafish) models to examine the effects of BPA in regulating the expression of genes involved in the thyroid hormone synthesis and of their transcriptional regulators at BPA doses as low as 10-9M, a dose that is environmentally pertinent and far below the one detected in infants plasma. In both systems we could detect an altered expression of the genes involved in thyroid hormones synthesis and of thyroid specific transcriptional factors in BPA dose and time dependent manner. Our results suggest that BPA exerts a direct effect on thyroid follicular cell. We show that these cells can "sense" very low amount of BPA. Thus they, potentially, represent an ideal in vitro system to develop assays to detect BPA and other pollutants with thyroid disrupting activity at level far below the ones considered to be environmental relevant. Moreover, this report may provide new insight into the mode of BPA-induced deregulation of physiological processes as well as on the extensively debated molecular pathways underlying its biological activities. © 2012 Elsevier Ireland Ltd

Carcinogenic risk and Bisphenol A exposure: A focus on molecular aspects in endoderm derived glands

Epidemiological and experimental evidence associates the exposure to Bisphenol A with the increase of cancer risk in several organs, including prostate. BPA targets different pathways involved in carcinogenicity including the Nuclear Receptors (i.e. estrogen and androgen receptors), stress regulated proteins and, finally, epigenetic changes. Here, we analyse BPA-dependent carcinogenesis in endoderm-derived glands, thyroid, liver, pancreas and prostate focusing on cell signalling, DNA damage repair pathways and epigenetic modifications. Mainly, we gather molecular data evidencing harmful effects at doses relevant for human risk (low-doses). Since few molecular data are available, above all for the pancreas, we analysed transcriptomic data generated in our laboratory to suggest possible mechanisms of BPA carcinogenicity in endoderm-derived glands, discussing the role of nuclear receptors and stress/NF-kB pathways. We evidence that an in vitro toxicogenomic approach might suggest mechanisms of toxicity applicable to cells having the same developmental origin. Although we cannot draw firm conclusions, published data summarized in this review suggest that exposure to BPA, primarily during the developmental stages, represents a risk for carcinogenesis of endoderm-derived glands

A Toxicogenomic Approach Reveals a Novel Gene Regulatory Network Active in In Vitro and In Vivo Models of Thyroid Carcinogenesis

Epidemiological and experimental studies emphasize the link between environmental chemicals exposure and thyroid cancer. However, this association is strongly debated and the mechanisms of action of environmental thyroid carcinogens still need to be identified. The analysis of in vitro transcriptomic data developed to investigate the effects of chlorpyrifos on immortalized thyrocytes highlighted the impaired expression of genes involved in endodermal carcinogenesis. This endodermal carcinogenic gene-network (ECGN, including Zfp36l2, Dmbt1, Ddit4), was validated in cellular and mouse models of thyroid carcinogenesis, characterized by the constitutive activation of the mitogen-activated protein kinase (MAPK) pathway and in immortalized thyrocytes exposed to tetrachlorodibenzo-p-dioxin (TCDD) and chlorpyrifos (CPF). The mRNA levels of Zfp36l2, Dmbt1 and Ddit4 were increased in models characterized by MAPK activation or following TCDD exposure, whereas they were inhibited by CPF exposure. Overall, the ECGN transcripts identify a novel gene-regulatory network associated with thyroid carcinogenesis promoted by genetic mutation or by environmental carcinogens. The latter have opposite effects on the modulation of the ECGN transcripts according to their mechanisms of action in promoting carcinogenesis. Therefore, the analyses of ECGN might be helpful in discriminating compounds that promote cellular survival associated or not to proliferation of thyrocytes

The myokine irisin is released in response to saturated fatty acids and promotes pancreatic β-cell survival and insulin secretion

This study explored the role of irisin as a new pancreatic β-cell secretagogue and survival factor and its potential role in the communication between skeletal muscle and pancreatic β-cells under lipotoxic conditions. Recombinant irisin stimulated insulin biosynthesis and glucosestimulated insulin secretion (GSIS) in a PKA-dependent manner and prevented saturated fatty acid-induced apoptosis in human and rat pancreatic β-cells, as well as in human and murine pancreatic islets, via AKT/BCL2 signaling. Treatment of myotubes with 0.5 mmol/L palmitate for 4 h, but not with oleate, promoted an increase in irisin release in the culture medium. Moreover, increased serum levels of irisin were observed in mice fed with a high-fat diet.Mouse serum rich in irisin and the conditioned medium from myotubes exposed to palmitate for 4 h significantly reduced apoptosis of murine pancreatic islets and insulinsecreting INS-1E cells, respectively, and this was abrogated in the presence of an irisin-neutralizing antibody. Finally, in vivo administration of irisin improved GSIS and increased β-cell proliferation. In conclusion, irisin can promote β-cell survival and enhance GSIS and may thus participate in the communication between skeletal muscle and β-cells under conditions of excess saturated fatty acids

ZFP36L2 Role in Thyroid Functionality

: Thyroid hormone levels are usually genetically determined. Thyrocytes produce a unique set of enzymes that are dedicated to thyroid hormone synthesis. While thyroid transcriptional regulation is well-characterized, post-transcriptional mechanisms have been less investigated. Here, we describe the involvement of ZFP36L2, a protein that stimulates degradation of target mRNAs, in thyroid development and function, by in vivo and in vitro gene targeting in thyrocytes. Thyroid-specific Zfp36l2-/- females were hypothyroid, with reduced levels of circulating free Thyroxine (cfT4) and Triiodothyronine (cfT3). Their hypothyroidism was due to dyshormonogenesis, already evident one week after weaning, while thyroid development appeared normal. We observed decreases in several thyroid-specific transcripts and proteins, such as Nis and its transcriptional regulators (Pax8 and Nkx2.1), and increased apoptosis in Zfp36l2-/- thyroids. Nis, Pax8, and Nkx2.1 mRNAs were also reduced in Zfp36l2 knock-out thyrocytes in vitro (L2KO), in which we confirmed the increased apoptosis. Finally, in L2KO cells, we showed an altered response to TSH stimulation regarding both thyroid-specific gene expression and cell proliferation and survival. This result was supported by increases in P21/WAF1 and p-P38MAPK levels. Mechanistically, we confirmed Notch1 as a target of ZFP36L2 in the thyroid since its levels were increased in both in vitro and in vivo models. In both models, the levels of Id4 mRNA, a potential inhibitor of Pax8 activity, were increased. Overall, the data indicate that the regulation of mRNA stability by ZFP36L2 is a mechanism that controls the function and survival of thyrocytes

Peripheral T3 signaling is the target of pesticides in zebrafish larvae and adult liver

The intra-tissue levels of thyroid hormones (THs) regulate organ functions. Environmental factors can impair these levels by damaging the thyroid gland and/or peripheral TH metabolism. We investigated the effects of embryon ic and/or long-life exposure to low-dose pesticides, ethylene thiourea (ETU), chlorpyrifos (CPF) and both combined on intra-tissue T4/T3 metabolism/signaling in zebrafish at different life stages. Hypothyroidism was evident in exposed larvae that showed reduced number of follicles and induced tshb mRNAs. Despite that, we found an increase in free T4 (fT4) and free T3 (fT3) levels/signaling that was confirmed by transcriptional reg ulation of TH metabolic enzymes (deiodinases) and T3-regulated mRNAs (cpt1, igfbp1a). Second-generation larvae showed that thyroid and TH signaling was affected even wh en not directly exposed, suggesting the role of parental exposure. In adult zeb rafish, we found that sex-dependent damage of hepatic T3 level/signaling was associated with liver steatosis, which was more pronounced in females, with sex-dependent alteration of transcripts codifying the key enzymes involved in ‘de novo lipogenesis’ and β-oxidation. We found impaired activation of liver T3 and PPARα/Foxo3a pathways whose deregulation was already involved in mammalian liver steatosis. The data emphasizes that the intratissue imbalance of the T3 level is due to thyroid endocrine disruptors (THDC) and suggests that the effect of a slight modification in T 3 signaling might be amplified by its direct regulation or crosstalk with PPARα/Foxo3a pathways. Because T3 levels define the hypothyroid/hyperthyroid status of each organ, our findings might explain the pleiotropic and site-dependent effects of pesticides